Well Kadabra can evolve to Alakazam which has 490 Base Stats and Chimecho only got 425.
Alakazam is The Fastest Psychic type Except Deoxys-Speed. He got a Huge SAtk base stat and who cares about Kadabras Atk stat no one has Pshysical moves on him.

So I would go with this Alakazam
____

Moveset for Alakazam

Psychic

Focus Blast

Shadow Ball

Grass Knot

Moveset For Chimecho

T-wave

Psychic

Recover

Shadow Ball

I Would go with Kadabra and trade it with a friend and Evolve it to A ALAKAZAM!

-Shadow Ball can be found at route 210 after obtaining rock smash.
-Psychic can be found at route 211 after getting rock climb, or can be learnt at level 40.
-Energy Ball can be found at route 226/ Calm Mind can be bought at Battle Tower.
-Signal Beam can be learnt by the Move Tutor/ Recover is learnt via level 30.

Chimecho is better

If you are near the beginning of the game, and just need a Psychic type.